1. Field of the Invention
The present invention relates to a communication scheme for supporting data transfer to a visited site of a mobile terminal which moves across a private network operated by a private address system and an Internet operated by a global address system.
2. Description of the Background Art
A router device is used in connecting between LANs, and plays a role of transferring data packets (datagrams) from one LAN to the other LAN. Each data packet contains a description of its source and final destination network layer addresses (such as IP addresses in the case of IP, for example) in addition to communication data to be transferred, and the router device determines an output interface (port number) and a next transfer target node (a host that is either a router device or a communication terminal) of each data packet according to its address information.
Here, a routing by the router device will be described for an exemplary case of transmitting IP packets from a terminal A to a terminal B on a network.
An IP packet sent out from the terminal A is routed within the Internet according to an IP address written in its packet header, and transmitted up to a subnet to which the terminal B belongs. At that point, whenever a router device within the Internet is passed through, an IP forwarding processing in a sequence of: reception of a datalink layer packetxe2x86x92conversion into an IP packetxe2x86x92processing of an IP header information, etc. and an output target determinationxe2x86x92conversion into a datalink layer packetxe2x86x92transmission of a datalink layer packet, is carried out with respect to an IP packet transmitted from the terminal A. Once it reaches to a router device of the final subnet, a logical address to physical address conversion is carried out by ARP (Address Resolution Protocol) (by obtaining a MAC address from an IP address, for example), and an IP packet is converted into a datalink layer packet by attaching a datalink layer header information such as MAC address, and this datalink layer packet is transmitted to the terminal B.
On the other hand, a technique for accommodating mobile terminals into the Internet-like network has been studied and developed. As one such mobile access technique, a scheme utilizing Mobile IP is known.
Mobile IP deals with the case where a user carrying a mobile terminal communicates while moving over the IP network across a plurality of subnets. In the case of communicating while moving over the IP network where the network address of the mobile terminal changes as the location of the terminal changes, there is a need to provide a scheme for managing a location of the terminal and transferring communication contents properly, and Mobile IP is a scheme that is proposed in order to fulfill that need. Mobile IP is a technique which makes the mobile terminal to appear to the other terminals as if it is connected at a location where it is normally expected to be located (a home address of a home network), regardless of a location at which the mobile terminal is connected on the network. Mobile IP has been promoted to RFC level by IETF in October, 1996.
In the following, the basic operation of Mobile IP will be described with reference to FIG. 1, which shows an exemplary network configuration in which a first network 100-1 and a second network 100-2 are connected through Internet 100-3. Here, each of these networks is assumed to be operated using global addresses.
In Mobile IP, a network (home network) 100-1 to which a mobile terminal (mobile host: MH) 103 is normally connected has a router called home agent (HA) 105 located therein. The mobile terminal 103 is assigned with a home address at the home network, which is managed by the home agent 105. Here, for the sake of explanation, it is assumed that the home address of the mobile terminal 103 is xe2x80x9c10.2xe2x80x9d and the address of its home agent 105 is xe2x80x9c10.1xe2x80x9d.
Next, suppose that the mobile terminal 103 moves and makes a connection at a visited site network 100-2. The visited site network 100-2 has a router called foreign agent (FA) 106 located therein. After moving, the mobile terminal 103 receives packets destined to the own node via this foreign agent 106. Here, for the sake of explanation, it is assumed that the IP address of the foreign agent 106 is xe2x80x9c20.1xe2x80x9d. In this case, the address xe2x80x9c20.1xe2x80x9d of the foreign agent 106 will be used as the current location address (called care-of address) of the mobile terminal 103.
In order to notify the current location of the own node, the mobile terminal 103 notifies the IP address xe2x80x9c20.1xe2x80x9d of the current location from the visited site to the home agent 105. Upon receiving this notification, the home agent 105 manages a correspondence between the home address xe2x80x9c10.2xe2x80x9d and the current location address xe2x80x9c20.1xe2x80x9d of the mobile terminal 103.
Now, Mobile IP assumes that there exists a correspondent host who does not know that the mobile terminal 103 has moved. This correspondent host (CH) 109 that tries to communicate with the mobile terminal 103 does not know that the mobile terminal 103 has moved so that it transmits packets destined to the home address xe2x80x9c10.2xe2x80x9d. However, the mobile terminal 103 is currently absent from the home network. Hence, the home agent 105 which manages this mobile terminal 103 intercepts (receives as a proxy) a packet destined to the home address xe2x80x9c10.2xe2x80x9d, and transfers it by encapsulating it into an IP packet destined to the current location address xe2x80x9c20.1xe2x80x9d that is registered in advance. The foreign agent 106 that is located at the address xe2x80x9c20.1xe2x80x9d takes out this packet from the encapsulated packet that is transferred thereto, and delivers it to the visiting mobile terminal 103 at the datalink layer. By such a mechanism, the mobile terminal 103 can receive a packet that would have been received by the own node at its original home network 100-1, even at its visited site.
In the opposite case where the mobile terminal 103 returns a packet to the correspondent host 109 from its current location, an IP packet is sent to the correspondent host 109 directly without going through the home agent 105. At that point, the home address xe2x80x9c10.2xe2x80x9d is used as a source address to be attached to that packet, rather than the current location (care-of) address xe2x80x9c20.1xe2x80x9d. In this way, it appears as if the mobile terminal 103 is continually connected to its home network, from the correspondent host 109, so that the influence of the moving can be eliminated entirely.
As described above, in Mobile IP, each node (correspondent host) on the network can access the mobile terminal 103 regardless of a location on the network at which the mobile terminal 103 is connected, by using the home address of the home network 103.
Now, in the Mobile IP scheme, a protocol is designed by assuming only a case where the mobile terminal moves within a single address space. That is, it has been assumed that the current location registration message (which is also referred to as the mobility registration message) from the visited site can reach the home agent of the home network without failure.
However, nowadays, in the case where a large organization makes Internet connections, it is rather rare to have global IP addresses allocated to all the nodes within the organization because of the shortage of IP addresses, and usually private addresses (see RFC 1597) are used for operation within the organization and the address conversion to global addresses are carried out at a time of communications with the external.
Thus, in such a case, Mobile IP can be utilized only within a range where the mobile terminal moves within a single address space. In other words, there has been a problem that Mobile IP cannot support those services in which the mobile terminal is allowed to move across networks operated by mutually different address systems.
FIG. 2 shows an exemplary case where Mobile IP cannot be utilized, which is a network model in which a communication service provider offers a service using mobile terminals that are capable of making Internet accesses. FIG. 2 shows an exemplary network configuration in which a private network 101 operated by a private address system and a global Internet 102-2 operated by a global address system are connected through Internet 102-1 operated by a global address system.
The number of global addresses that are allocated to one communication service provider is limited, so that communications using private addresses will be carried out within the private network 101 operated by the communication service provider. This service can possibly be required to support not only data transfer in the case where the mobile terminal 103 moved from the home network 101a to another subnet 101b and accesses to servers 201 and 202 of the private network 101 by the mobile terminal 103, but also accesses to a server 203 which is generally connected to the global Internet 102-1 from within the private network 101 by using a network address translation device 104 having a network address translation (NAT) function, and direct communications by the mobile terminal 103 that has moved to the global Internet 102-2 in a global region.
However, when the mobile terminal 103 which has its home network in a private region moves into a global region, Mobile IP cannot be used. On the contrary, when the mobile terminal which has its home network in a global region moves into a private region, Mobile IP also cannot be used.
In such a network model, it is not sufficient to realize a simple packet exchange between the private network and the global Internet, and it is also necessary to maintain currently carried out communications by utilizing the properties of Mobile IP even in a case where the mobile terminal that had been connected to the private network shortly before has now moved to the global Internet or vise versa.
In order to realize that, it is necessary to carry out the routing control of communication packets by recognizing the current location to which the mobile terminal has moved, comprehending a relative relationship with respect to a location to which the mobile terminal had been connected shortly before, and carrying out the necessary global to private address translation via the entrance of the private network.
As described above, in general, in order to support the mobile terminal which moves across the private network operated by the communication service provider and the global Internet by utilizing the Mobile IP scheme, it is necessary to provide a scheme for controlling a location to be regarded as the current home network according to the current location and the immediately previous location of the mobile terminal and a way of commanding transfer of packets to the current location with respect to the immediately previous home network, and for realizing the routing control up to the final destination by receiving the transmitted or transferred packet at the border between the private network and the global network and converting it into appropriate format.
Thus, in the case of supporting a service in which the mobile terminal can move across networks operated by mutually different address systems, the conventionally known mobile access technique for Internet-like network such as the usual mobile management by Mobile IP in a single address space is insufficient, and there is a need for a mechanism which can properly account for two types of address spaces such as the private network operated by the private address system managed by the communication service provider and the general global Internet, and realize not only the packet exchange across their border but also the proper routing control of packets up to the current location even when the mobile terminal moves across their border.
It is therefore an object of the present invention to provide a communication scheme for the mobile terminal that moves across a plurality of networks operated by mutually different address systems, which is capable of supporting the moving by the mobile terminal within each network and transferring data packets having the former address of the mobile terminal as their destination to the current location of the mobile terminal even when the mobile terminal moves across these networks.
According to one aspect of the present invention there is provided a communication system for supporting data packet transfer with respect to mobile terminals capable of carrying out communications while moving among networks, in a first network and a second network which are operated by mutually different address systems and which are capable of accommodating the mobile terminals, the communication system comprising: a packet relay device having a first interface connected with the first network and a second interface connected with the second network; a first router device provided at a first subnet in the first network, having a function for transferring packets destined to a home address of each mobile terminal belonging to the first subnet to a care-of address of each mobile terminal; and a second router device provided at a second subnet in the second network; wherein when a mobile terminal has moved from the first network to the second network, the first router device transfers packets destined to an original home address on the first subnet of the mobile terminal by setting an address of the first interface of the packet relay device as a care-of address of the mobile terminal, the packet relay device transfers the packets received from the first router device at the first interface to the second router device through the second interface, and the second router device transfers the packets received from the packet relay device to a current location address of the mobile terminal.
According to another aspect of the present invention there is provided a method of data packet transfer in a communication system for supporting data packet transfer with respect to mobile terminals capable of carrying out communications while moving among networks, in a first network and a second network which are operated by mutually different address systems and which are capable of accommodating the mobile terminals, the communication system including a packet relay device having a first interface connected with the first network and a second interface connected with the second network, a first router device provided at a first subnet in the first network, the first router device having a function for transferring packets destined to a home address of each mobile terminal belonging to the first subnet to a care-of address of each mobile terminal, and a second router device provided at a second subnet in the second network, the method comprising the steps of: (a) when a mobile terminal has moved from the first network to the second network, transferring packets destined to an original home address of the mobile terminal on the first subnet from the first router device by setting an address of the first interface of the packet relay device as a care-of address of the mobile terminal; (b) transferring the packets received by the packet relay device from the first router device at the first interface to the second router device through the second interface; and (c) transferring the packets received by the second router device from the packet relay device to a current location address of the mobile terminal.
According to another aspect of the present invention there is provided a router device for use in a communication system for supporting data packet transfer with respect to mobile terminals capable of carrying out communications while moving among networks, in a first network and a second network which are operated by mutually different address systems and which are capable of accommodating the mobile terminals, the communication system including a packet relay device having a first interface connected with the first network and a second interface connected with the second network, the router device being provided at a subnet in the first network and comprising: a first management unit for managing an original home address on the subnet of a mobile terminal for which the subnet is an original home network; a second management unit for managing a care-of address of the mobile terminal; and a transfer unit for receiving packets destined to the original home address managed by the first management unit on behalf of the mobile terminal, and transferring the packets to the care-of address managed by the second management unit, when the mobile terminal is currently not located at the original home address, such that when the mobile terminal has moved from the first network to the second network, the router device transfers packets destined to the original home address by setting an address of the first interface of the packet relay device as the care-of address.
According to another aspect of the present invention there is provided a router device for use in a communication system for supporting data packet transfer with respect to mobile terminals capable of carrying out communications while moving among networks, in a first network and a second network which are operated by mutually different address systems and which are capable of accommodating the mobile terminals, the communication system including a packet relay device having a first interface connected with the first network and a second interface connected with the second network, the router device being provided at a subnet in the second network and comprising: a first management unit for managing a new home address on the subnet of a mobile terminal for which the subnet is a new home network; a second management unit for managing a current location address of the mobile terminal; a message transfer unit for transferring to the packet relay device a pair information on an original home address that has been allocated to the mobile terminal in the first network and the new home address of the mobile terminal transmitted from the mobile terminal and managed by the first management unit, when the mobile terminal has moved from the first network to the second network, such that the packer relay device transfers packets destined to the original home address and received at the first interface to the router device through the second interface; and a packet transfer unit for transferring the packets received from the packet relay device to the current location address of the mobile terminal managed by the second management unit.
According to another aspect of the present invention there is provided a packer relay device for use in a communication system for supporting data packet transfer with respect to mobile terminals capable of carrying out communications while moving among networks, in a first network and a second network which are operated by mutually different address systems and which are capable of accommodating the mobile terminals, the communication system including a first router device provided at a first subnet in the first network and a second router device provided at a second subnet in the second network, the packet relay device being provided between the first network and the second network and comprising: a first interface connected with the first network; a second interface connected with the second network; a message reception unit for receiving through the second interface a pair information on an original home address of a mobile terminal on the first subnet and a new home address acquired by the mobile terminal on the second subnet when the mobile terminal moves from the first network to the second network, the pair information being notified by the mobile terminal; a message analysis unit for obtaining the original home address and the new home address along with information on the first and second router devices, by analyzing the pair information received by the message reception unit; a message transmission unit for transmitting a message to the first router device through the first interface, such that the first router device transfers packets destined to the original home address to the first interface; and a packet transfer unit for transferring the packets received at the first interface to the second router device through the second interface by using the new home address, such that the second router device transfers the packets to the mobile terminal.
According to another aspect of the present invention there is provided a computer usable medium having computer readable program code means embodied therein for causing a computer to function as a router device for use in a communication system for supporting data packet transfer with respect to mobile terminals capable of carrying out communications while moving among networks, in a first network and a second network which are operated by mutually different address systems and which are capable of accommodating the mobile terminals, the communication system including a packet relay device having a first interface connected with the first network and a second interface connected with the second network, the router device being provided at a subnet in the first network and the computer readable program code means includes: first computer readable program code means for causing said computer to manage an original home address on the subnet of a mobile terminal for which the subnet is an original home network; second computer readable program code means for causing said computer to manage a care-of address of the mobile terminal; and third computer readable program code means for causing said computer to receive packets destined to the original home address managed by the first computer readable program code means on behalf of the mobile terminal, and transfer the packets to the care-of address managed by the second computer readable program code means, when the mobile terminal is currently not located at the original home address, such that when the mobile terminal has moved from the first network to the second network, the router device transfers packets destined to the original home address by setting an address of the first interface of the packet relay device as the care-of address.
According to another aspect of the present invention there is provided a computer usable medium having computer readable program code means embodied therein for causing a computer to function as a router device for use in a communication system for supporting data packet transfer with respect to mobile terminals capable of carrying out communications while moving among networks, in a first network and a second network which are operated by mutually different address systems and which are capable of accommodating the mobile terminals, the communication system including a packet relay device having a first interface connected with the first network and a second interface connected with the second network, the router device being provided at a subnet in the second network and the computer readable program code means includes: first computer readable program code means for causing said computer to manage a new home address on the subnet of a mobile terminal for which the subnet is a new home network; second computer readable program code means for causing said computer to manage a current location address of the mobile terminal; third computer readable program code means for causing said computer to transfer to the packet relay device a pair information on an original home address that has been assigned to the mobile terminal in the first network and the new home address of the mobile terminal transmitted from the mobile terminal and managed by the first computer readable program code means, when the mobile terminal has moved from the first network to the second network such that the packer relay device transfers packets destined to the original home address and received at the first interface to the router device through the second interface; and fourth computer readable program code means for causing said computer to transfer the packets received from the packet relay device to the current location address of the mobile terminal managed by the second computer readable program code means.
According to another aspect of the present invention there is provided a computer usable medium having computer readable program code means embodied therein for causing a computer to function as a packer relay device for use in a communication system for supporting data packet transfer with respect to mobile terminals capable of carrying out communications while moving among networks, in a first network and a second network which are operated by mutually different address systems and which are capable of accommodating the mobile terminals, the communication system including a first router device provided at a first subnet in the first network and a second router device provided at a second subnet in the second network, the packet relay device being provided between the first network and the second network and having a first interface connected with the first network and a second interface connected with the second network, and the computer readable program code means includes: first computer readable program code means for causing said computer to receive a pair information on an original home address of a mobile terminal on the first subnet and a new home address acquired by the mobile terminal on the second subnet when the mobile terminal moves from the first network to the second network, the pair information being notified by the mobile terminal through the second interface; second computer readable program code means for causing said computer to obtain the original home address and the new home address along with information on the first and second router devices, by analyzing the pair information received by the first computer readable program code means; third computer readable program code means for causing said computer to transmit a message to the first router device through the first interface, such that the first router device transfers packets destined to the original home address to the first interface; and fourth computer readable program code means for causing said computer to transfer the packets received at the first interface to the second router device through the second interface by using the new home address, such that the second router device transfers the packets to the mobile terminal.
Other features and advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings.